<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>containerClass</title>
<style>
  .ccc {
    border: 1px solid pink;
  }
</style>
</head>
<body>
<canvas id="canvasBox"></canvas>

<script src="../../script/fabric.js"></script>
<script>
  let canvas = new fabric.Canvas('canvasBox', {
    containerClass: 'ccc'
  })
</script>
</body>
</html>